Diodes may be used for isolation purposes. For example, in Local Interconnect Network Bus-systems (LINBus) that are often used in cars, diodes may be used to isolate batteries to prevent leakage.
A conventional isolation diode may be built as a part of an integrated circuit, which includes a p-type substrate and an N-type Buried Layer (NBL) over the substrate. The anode of the diode may include a High-Voltage P-type Well (HVPW) over the NBL and a P+ region over the HVPW. The cathode of the diode may include a High-Voltage N-type Well (HVNW) over the NBL and an N+ region over the HVNW. To prevent the cathode from being directly connected to the NBL, a Deep P-Well (DPW) may be formed at a middle level or a bottom level of the HVNW, so that the cathode, which is of N type, is isolated from the NBL by the DPW.
The conventional isolation diode, however, suffers from leakage currents when the diode is forwardly biased. The anode (p-type), the NBL, and the p-type substrate form a PNP bipolar junction transistor, which may be turned on when the diode is forwardly biased. Accordingly, a leakage current may flow from the anode to the substrate.